Probably, a hybrid approach combining a first scrutiny of possible configurations and a subsequent CFD analysis could be an answer. Eventually, the design may be modified in order to mitigate any problem that could be revealed by the CFD results, but there is no way to state that all possible design options have been explored. The complete geometry of the ejector must be known in advance before any CFD analysis is attempted. However, it must be stressed that CFD is not a design tool.
The only way to get a complete picture of the flow field is to analyze the ejector by a Computational Fluid Dynamics (CFD) approach. Indeed, a detailed analysis of the influence of geometrical details on the supersonic flow is not feasible with analytical tools. The effect of other details, like the presence of fillets between conical and cylindrical parts, is also neglected.
Other elements, like the mixing zone length or the angle of the secondary flow inlet, are left to the experience of the designer. In many cases, ejectors are designed in a rather empirical way, and the only elements of the ejector geometry that receive a calculation effort are the main flow sections. Ejector design may be performed at various levels of complexity.
